A PCT application WO2011106232 shows a typical way of manufacturing a ceramic element that includes mixing a premixture with other components in order to obtain a batch mixture containing a cellulose ingredient and an aluminium component; the addition of liquid to the batch mixture in order to form the batch; shaping the batch to a form of body; firing the shaped body in order to form the ceramic element. This typical way has certain defects, for example the inaccuracies resulting from shaping the body under a relatively low pressure and relatively large dimensions of the shaped element in order to ensure appropriate electro-insulating properties.
Recently, there has been developed a technology of isostatic pressing that enables to shape ceramic elements effectively. It consists in treating a ceramic mixture under isostatic pressure in a chamber with a liquid under high pressure. The pressure is exerted on the material from all directions.
A U.S. Pat. No. 4,938,673 describes hot isostatic pressing, wherein an element is prepared from a mixture containing a powdered coupled and a first powdered insulator, and after that the element is immersed in a second powdered insulator in a compressible container, and then the element is placed inside a pressurized vessel to which a microwave energy is supplied to raise a temperature of the element, and then the element is compressed by using a liquid medium supplied under pressure.
The technology of isostatic pressing of ceramic elements has been applied so far for relatively large components, such as ceramic chimneys that require a moderate dimensional accuracy.
A Russian patent document RU2318657 presents a method for manufacturing of a ceramic insulator. This insulator is a solid element. In this method, a mould is filled with a ceramic powder and, while filling, the vibrations of the whole mould are induced. Then the mould is closed and pressed to achieve porosity of the finished element at the level of 20-36%. This process has several disadvantages. First, the produced elements are solid elements and not pipes, therefore they have large mass and are fairly expensive to manufacture. The final, relatively high porosity of up to 36% induces large dimensional inaccuracies when fired and thus the produced element requires additional mechanical treatment by using costly diamond tools in order to obtain the desired dimensional tolerance. In addition, vibrations of the whole mould require high power vibrators.